A mobile crane is provided with a winch device configured to wind up and down a hoisted load. A mainly used winch device is a winch device driven by a hydraulic actuator such as a hydraulic motor. However, a hydraulic actuator generally has low energy efficiency. It is therefore proposed to mount, on a crane, an electrically driven winch device in which an electric actuator having relatively high energy efficiency is used as a driving source for the electrically driven winch device. For example, motorization of a winch device is progressing for a tower crane configured to perform crane work in a state fixed to a floor of a building under construction.
Patent Literature 1 discloses a climbing crane which is an example of a tower crane. This climbing crane is provided with an electrically driven winch device having a winch drum, and two electric motors configured to drive the winch drum to rotate. In this electrically driven winch device, two electric motors are disposed separately on both axial sides of the winch drum and torque from respective electric motors is input into the winch drum from the both sides, in order to prevent generation of local torsion at an input shaft of the winch drum or at the winch drum itself.
The electrically driven winch device of Patent Literature 1 has an advantage that large hoisting capacity can be secured, since the winch drum is rotated with torque output from two electric motors. However, the axial dimension of an electrically driven winch device increases when employing a structure in which two electric motors are disposed on both axial sides of the winch drum. Accordingly, it becomes impossible to employ an electrically driven winch device having such a structure in a case where there is restriction regarding an installation space. Moreover, when such an electrically driven winch device is mounted on a mobile crane, a vehicle width thereof becomes large, and it may possibly become necessary to employ disassembling transportation in transporting the mobile crane using a public road, according to a legal request on vehicle width limitation.